[tkreuzer] 70430: [CRT] Fix x86 asm implementation of strlen / wcslen.

Author: tkreuzer
Date: Sat Dec 26 20:34:15 2015
New Revision: 70430

URL: http://svn.reactos.org/svn/reactos?rev=70430&view=rev
Log:
[CRT]
Fix x86 asm implementation of strlen / wcslen.

Modified:
    trunk/reactos/lib/sdk/crt/string/i386/tcslen.inc

Modified: trunk/reactos/lib/sdk/crt/string/i386/tcslen.inc
URL: http://svn.reactos.org/svn/reactos/trunk/reactos/lib/sdk/crt/string/i386/tcs...
==============================================================================
--- trunk/reactos/lib/sdk/crt/string/i386/tcslen.inc	[iso-8859-1] (original)
+++ trunk/reactos/lib/sdk/crt/string/i386/tcslen.inc	[iso-8859-1] Sat Dec 26 20:34:15 2015
@@ -7,23 +7,34 @@

FUNC _tcslen
     FPO 0, 1, 1, 1, 0, FRAME_FPO
+
+    /* Save edi and eflags (according to the x86 ABI, we don't need to do that
+       but since the native function doesn't change the direction flag, we don't
+       either */
     push edi
-    mov edi, [esp + 8]
+    pushfd
+
+    /* Load the string pointer into edi */
+    mov edi, [esp + 12]
+
+    /* Set eax to 0, since we want to compare with 0 */
     xor eax, eax
-    test edi, edi
-    jz _tcslen_end

+    /* Set ecx to -1 (i.e. 0xFFFFFFFF) */
     mov ecx, -1
+
+    /* Clear direction flag */
     cld

+    /* Now compare the characters until a 0 is found */
     repne _tscas

+    /* Calculate the count (eax = -ecx - 1) */
     not ecx
-    dec ecx
+    lea eax, [ecx-1]

-    mov eax, ecx
-
-_tcslen_end:
+    /* Restore eflags/edi and return the result */
+    popfd
     pop edi
     ret
 ENDFUNC